1. Field of the Invention
The present invention relates to a film forming apparatus for forming a carbon film on an object such as a semiconductor wafer, and a method of operating the same.
2. Description of the Related Art
Generally, in order to form an integrated circuit (IC), such as a semiconductor IC, various processes, such as a film forming process, an etching process, an oxidation diffusion process, and an annealing process, are repeatedly performed on a semiconductor wafer formed of a silicon substrate, etc. Here, according to an example of an etching process, a thin film formed of any one of various materials is conventionally used as an etching mask in order to perform a micro-size process. Recently, there are cases where a carbon film is used as an etching mask, i.e., a sacrificial film (for example, Patent Documents 1 and 2). This is because the carbon film is satisfactorily deposited even on a side wall of a recess portion of a pattern of a wafer surface, for example, in the film forming process, compared to other etching mask materials, thereby increasing a step coverage.
If the carbon film is, for example, polycrystallized and has the satisfactory step coverage as described above, the utility of the carbon film is increased under a current situation where a design rule is strict according to a further decrease of a line width or the like and the progress of miniaturization.
However, when the carbon film is to be formed on a semiconductor wafer, a material gas, for example, ethylene is introduced into a processing container formed of a quartz material under a depressurized atmosphere. Here, as a countermeasure against particles or in order to maintain the reproducibility of a film forming process, the material gas is introduced into the processing container without accommodating the wafer in the processing container before performing the film forming process, and then a carbon film in an amorphous state is formed as a pre-coating film on an inner surface of the processing container and surfaces of members formed of a quartz material in the processing container, for example, a wafer boat holding the semiconductor wafer. After forming the pre-coating film, the semiconductor wafer is held by the wafer boat and then carried (loaded) into the processing container, and a carbon film is formed on the semiconductor wafer.
However, since the carbon film does not have a satisfactory adhesion to quartz (SiO2), the pre-coating film or the carbon film deposited on the pre-coating film during performing the film forming process on the semiconductor easily peels off, thereby generating particles.    (Patent Document 1) Japanese Laid-Open Patent Publication No. 2007-523034    (Patent Document 2) Japanese Laid-Open Patent Publication No. 2011-181903